WCrY smart alloys as advanced plasma-facing materials – Exposure to steady-state pure deuterium plasmas in PSI-2

Schmitz, J.; Litnovsky, A.; Klein, F.; Wegener, T.; Tan, Xiao–Yue; Rasiński, M.; Mutzke, A.; Hansen, P.; Kreter, A.; Pospieszczyk, A.; Möller, S.; Coenen, J. W.; Linsmeier, Ch.; Breuer, U.; González‐Julián, Jesús; Bram, Martin

doi:10.1016/j.nme.2018.05.002

Cited by 24 publications

(33 citation statements)

References 12 publications

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“…4c) as well as a WCrY sample exposed to pure D plasma at an ion energy of 120 eV in an earlier reported experiment (Fig. 4d) [8]. SEM images of the WCrY sample after D + Ar plasma show elongated craters along the grain boundaries and small black holes on the surface.…”

Section: Plasma Exposuresupporting

confidence: 57%

“…Results were reported in Ref. [8]. For the exposure at 220 eV, W sputtering by D and Cr transports to the surface led to an enhanced volume loss of WCrY samples as compared to simultaneously exposed pure W samples.…”

Section: Introductionmentioning

confidence: 75%

“…A more detailed description of the analytic techniques used can be found in Ref. [8]. During the plasma exposure, different in situ diagnostics are used: with a Langmuir probe, the plasma parameters such as the ion flux incident to the target or the plasma potential are monitored.…”

Section: Plasma Exposurementioning

confidence: 99%

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Argon-seeded plasma exposure and oxidation performance of tungsten-chromium-yttrium smart alloys

et al. 2019

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Tungsten-chromium-yttrium (WCrY) smart alloys are foreseen as the first wall material for future fusion devices such as Demonstration Power Plant (DEMO). While suppressing W oxidation during accidental conditions, they should behave like pure W during plasma operation due to preferential sputtering of the lighter alloying elements Cr, Y, and W enrichment of the surface. In this paper, the erosion performance of WCrY and W samples simultaneously exposed to deuterium (D) plasma with the addition of 1% of the projectile ions being argon (Ar) ions at an ion energy of 120 eV is compared. With reference to the previous experiments at 120 eV in pure D plasma, the erosion for both WCrY and W is enhanced by a factor of ~ 7. Adding Ar to the D plasma suppresses significant W enrichment previously found for pure D plasma. To investigate the impact of the plasma exposure onto the oxidation performance, plasma-exposed and non-exposed reference samples were oxidised in a dry atmosphere. Results show, on the one hand, that the oxidation suppression of WCrY in comparison to pure W is preserved during the plasma performance. On the other hand, it becomes evident that edge effects imposed by the geometry of the samples used in plasma experiments play a significant role for the oxidation behaviour.

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Section: Plasma Exposuresupporting

confidence: 57%

Section: Introductionmentioning

confidence: 75%

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Argon-seeded plasma exposure and oxidation performance of tungsten-chromium-yttrium smart alloys

et al. 2019

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“…WCrY alloys were recently developed and tested in laboratory experiments (oxidation resistance) and in a plasma environment [5]. Plasma exposure of WCrY samples in the linear plasma device PSI-2 and subsequent analysis by secondary ion mass spectrometry confirm surface enrichment of W caused by preferential sputtering of Cr [6]. The plasma exposure in these experiments uses a pure D plasma with sample biasing between 120 V to 220 V and is performed at temperatures between 900 K and 1000 K, which is a typical temperature range estimated for the first wall during operation of a fusion power plant and temperatures of the divertor tiles are probably even higher.…”

Section: Introductionmentioning

confidence: 99%

Segregation and preferential sputtering of Cr in WCrY smart alloy

Koslowski

Schmitz

Linsmeier

2020

Nuclear Materials and Energy

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The temperature driven segregation of Cr to the surface of the tungsten-based WCrY alloy is analysed with low energy ion scattering of He + ions with an energy of 1 keV in the temperature range from room temperature to 1000 K. Due to the high surface sensitivity, these measurements probe only the composition of the outermost monolayer. The surface concentration of Cr increases slightly when the temperature of the sample is increased up to 700 K and exhibits a much stronger increase when the sample temperature is further raised. The segregation enthalpy for Cr is obtained from the Langmuir-McLean relation and amounts to 0.7 eV. The surface concentration of Y shows a similar behaviour to the Cr concentration. The temperature thresholds between slow and accelerated surface density increases for Cr and Y are nearly the same. At a temperature of 1000 K the low energy ion scattering detects almost no W on the surface. The modified surface composition due to the segregated species, i.e. the mixed Cr/Y layer, stays stable during cool-down of the sample. Preferential sputtering is investigated using ion bombardment of 250 eV D atoms, resulting in an increase of the W surface density at room temperature. This effect is counteracted at elevated temperatures where segregation replenishes the lighter elements on the surface and prevents the formation of an all-W surface layer. The flux of segregating Cr atoms towards the surface is evaluated from the equilibrium between sputter erosion and segregation.

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“…% Y. Further, the performance of smart alloys in humid environment [35], and the performance under plasma exposure [36] were investigated. Currently, there is a lack on the understanding of the detailed mechanisms yielding the oxidation resistance of smart alloys.…”

Section: Introductionmentioning

confidence: 99%

On Oxidation Resistance Mechanisms at 1273 K of Tungsten-Based Alloys Containing Chromium and Yttria

Klein

Wegener

Litnovsky

et al. 2018

Metals

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Tungsten (W) is currently deemed the main candidate for the plasma-facing armor material of the first wall of future fusion reactors, such as DEMO. Advantages of W include a high melting point, high thermal conductivity, low tritium retention, and low erosion yield. However, was an accident to occur, air ingress into the vacuum vessel could occur and the temperature of the first wall could reach 1200 K to 1450 K due to nuclear decay heat. In the absence of cooling, the temperature remains in that range for several weeks. At these temperatures, the radioactive tungsten oxidizes and then volatilizes. Smart W alloys are therefore being developed. Smart alloys are supposed to preserve properties of W during plasma operation while suppressing tungsten oxide formation in case of an accident. This study focuses on investigations of thin film smart alloys produced by magnetron sputtering. These alloys provide an idealistic system with a homogeneous distribution of the elements W, chromium (Cr), and yttrium (Y) on an atomic scale. The recommended composition is W with 12 weight % of Cr and 0.5 weight % of Y. Passivation and a suppression of WO 3 sublimation is shown. For the first time, the mechanisms yielding the improved oxidation resistance are analyzed in detail. A protective Cr 2 O 3 layer forms at the surface. The different stages of the oxidation processes up to the failure of the protective function are analyzed for the first time. Using 18 O as a tracer, it is shown for the first time that the oxide growth occurs at the surface of the protective oxide. The Cr is continuously replenished from the bulk of the sample, including the Cr-rich phase which forms during exposure at 1273 K. A homogenous distribution of yttria within the W-matrix, which is preserved during oxidation, is a peculiarity of the analyzed alloy. Further, an Y-enriched nucleation site is found at the interface between metal and oxide. This nucleation sites are deemed to be crucial for the improved oxidation resistance.

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WCrY smart alloys as advanced plasma-facing materials – Exposure to steady-state pure deuterium plasmas in PSI-2

Cited by 24 publications

References 12 publications

Argon-seeded plasma exposure and oxidation performance of tungsten-chromium-yttrium smart alloys

Argon-seeded plasma exposure and oxidation performance of tungsten-chromium-yttrium smart alloys

Segregation and preferential sputtering of Cr in WCrY smart alloy

On Oxidation Resistance Mechanisms at 1273 K of Tungsten-Based Alloys Containing Chromium and Yttria

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